The present invention relates to integrally molded articles of polyamide resins, particularly, it relates to integrally molded articles of polyamide resins integrated by injection welding.
Since polyamide resins are excellent in many properties such as mechanical properties, heat resistance, chemical resistance and wear resistance, they are used as a substitute material for metals such as iron, zinc and aluminum. Usually, various commercial articles are molded with polyamide resins by injection molding. However, in the case of certain types of molded articles, for example, hollow molded articles, it is impossible to mold the article with one normal mold.
Recently, there are many attempts to use polyamide resins for the hollow molded parts such as intake manifold of automobile engine, intake resonator, reservoir tank, etc. For producing such molded articles, there is used, for instance, a method in which two segments of a hollow molded article to be produced are first molded and these segments are welded by suitable means such as vibration welding. However, the shape of the segments that can be welded together by vibration welding or other means is restricted, and it is difficult by this method to obtain the resin molded articles of a complex configuration.
On the other hand, according to injection welding in which the segments formed by primary molding are set in a mold cavity and resin is injection molded along the butted edges of the segments to weld them together, the restriction on the shape of the segments is mild and the molded articles having a complex configuration can be obtained relatively easily. However, weld strength of the articles obtained by injection welding is generally low as compared with the articles produced by vibration welding, and in manufacture of the hollow tubes, such as intake manifold, which have the possibility to face elevation of internal pressure due to backfire of the engine or other causes, it is difficult to obtain the articles with high reliability.
As a result of the present inventors' earnest studies to solve the above problem, it has been found that the integrally molded articles of polyamide resins obtained by injection welding the moldings of a polyamide resin composition(s) prepared by blending glass fiber and nigrosine or a nigrosine derivative in the specified percentages in a polyamide resin have excellent weld strength.
The present invention has been attained on the basis of the above finding.